Entering the Time

If no reference clock is available, you have the option of adopting the system time from the PC. The device resets the time during a restart.

Note: When setting the time in zones with summer and winter times, make an adjustment for the local offset, if applicable.

The SNTP client can also get the SNTP server IP address and the local offset from a DHCP server.

The NTP client gets its NTP server IP address exclusively from the

Basic Settings 4.4 Synchronizing the System Time in the Network

 Select the Time:Basic Settings dialog.

With this dialog you can enter time-related settings.

 The “System time (UTC)” displays the time with reference to the coordinated world time scale UTC (Universal Time Coordinated).

The display is the same worldwide. Local time differences are not taken into account.

Possible sources of the system time (UTC) are: local, sntp and ntp, see “Time source”.

 The devices calculates the “system time” from the “system time (UTC)” and the “local offset” (the local time difference from UTC).

“System time” = “System time (UTC)” + “Local offset”.

 “Time Source” displays the source of the system time (UTC). The device automatically selects the available source with the greatest accuracy.

Possible sources are: local, sntp and ntp.

– The source is initially local. This is the system clock of the device.

– If you have activated the SNTP client and if the device receives a valid SNTP packet, the device sets its time source to sntp.

– If you have activated the NTP client and if the client has synchronized itself, the device sets its time source to ntp.

 With “Set time from PC”, the device takes the PC time as the system time and calculates the IEEE 1588 / SNTP time using the local time difference.

“IEEE 1588 / SNTP time” = “System time” - “Local offset”

 The “local offset” is for displaying/entering the time difference between the local time and the “System Time (UTC)”.

With ”Set offset from PC“, the device determines the time zone on your PC and uses it to calculate the local time difference.

enable Switch to the privileged EXEC mode.

configure Switch to the Configuration mode.

sntp time <YYYY-MM-DD HH:MM:SS>

Set the system time of the device.

Basic Settings 4.4 Synchronizing the System Time in the Network

4.4.2 SNTP

 Description of SNTP

The Simple Network Time Protocol (SNTP) enables you to synchronize the system time in your network.

The device supports the SNTP client and the SNTP server function.

The SNTP server makes the UTC (Universal Time Coordinated) available. UTC is the time relating to the coordinated world time measurement. The time displayed is the same worldwide. Local time differences are not taken into account.

SNTP uses the same packet format as NTP. In this way, an SNTP client can receive the time from an SNTP server as well as from an NTP server.

Figure 15: SNTP cascade

 Preparing the SNTP Configuration

 To get an overview of how the time is passed on, draw a network plan with all the devices participating in SNTP. When planning, bear in mind that the accuracy of the time depends on the signal runtime.

GPS

Basic Settings 4.4 Synchronizing the System Time in the Network

Figure 16: Example of SNTP cascade

 Enable the SNTP function on all devices whose time you want to set using SNTP.

The SNTP server of the device responds to Unicast requests as soon as it is enabled.

 If no reference clock is available, specify a device as the reference clock and set its system time as accurately as possible.

Note: For accurate system time distribution with cascaded SNTP servers and clients, use only network components (routers, switches, hubs) in the signal path between the SNTP server and the SNTP client which forward SNTP packets with a minimized delay.

 Configuring SNTP

 Select the Time:SNTP dialog.

 Operation

 In this frame you switch the SNTP function on/off globally.

Note: If you switch SNTP on when NTP is already active on the device, the device reports an error.

To switch SNTP on, first deactivate NTP.

On delivery, NTP is switched off.

GPS

Basic Settings 4.4 Synchronizing the System Time in the Network

 SNTP Status

 The “Status message” displays statuses of the SNTP client as one or more test messages, e.g. Server 2 not

responding.

 Configuration SNTP Client

 In “External server address” you enter the IP address of the SNTP server from which the device periodically requests the system time.

 In “Redundant server address” you enter the IP address of an additional SNTP server. The device periodically requests from this server the system time if it does not receive a response from the server to a request from the “External server address” within 1 second.

Note: If you are receiving the system time from an external/

redundant server address, you do not accept any SNTP

Broadcast packets (see below). You thus ensure that the device uses the time of the server entered.

 In “Server request interval” you specify the interval at which the device requests SNTP packets (valid entries: 1 s to 3,600 s, on delivery: 30 s).

 With “Accept SNTP Broadcasts” the device takes the system time from SNTP Broadcast/Multicast packets that it receives.

 Configuration SNTP Server

 In “Anycast destination address” you enter the IP address to which the SNTP server of the device sends its SNTP packets (see table 6).

 In “Anycast send interval” you specify the interval at which the device sends SNTP packets (valid entries: 1 s to 3,600 s, on delivery: 120 s).

 With “Disable Server at local time source” the device disables the SNTP server function if the source of the time is local (see Time:Basic Settings dialog).

Basic Settings 4.4 Synchronizing the System Time in the Network

4.4.3 NTP

The Network Time Protocol (NTP) enables you to synchronize the system time in your network. The device supports the NTP client and the NTP server function.

With NTP, the device can determine the time more accurately than with SNTP. Thus, as an NTP server it can also provide a more accurate time.

The NTP and SNTP packet formats are identical.

In contrast to the SNTP client, the NTP client uses multiple NTP servers and a more complex algorithm for the synchronization. It can thus determine the time more accurately. Therefore, the synchronization of the NTP client can take longer than an SNTP client.

Only use NTP if you are sure that require this increased accuracy.

IP destination address Send SNTP packet to

0.0.0.0 Nobody

Unicast address (0.0.0.1 - 223.255.255.254) Unicast address Multicast address (224.0.0.0 - 239.255.255.254),

especially 224.0.1.1 (NTP address) Multicast address

255.255.255.255 Broadcast address

Table 6: Destination address classes for SNTP and NTP packets

Device 192.168.1.1 192.168.1.2 192.168.1.3

Operation On On On

Server destination address 0.0.0.0 0.0.0.0 0.0.0.0

Server VLAN ID 1 1 1

Send interval 120 120 120

Client external server address 192.168.1.0 192.168.1.1 192.168.1.2

Request interval 30 30 30

Accept Broadcasts No No No

Table 7: Settings for the example (see fig. 16)

Basic Settings 4.4 Synchronizing the System Time in the Network

The NTP server makes the UTC (Universal Time Coordinated) available.

UTC is the time relating to the coordinated world time measurement. The time displayed is the same worldwide. Local time differences are not taken into account.

The NTP client obtains the UTC from one or more external NTP servers.

Note: To obtain as accurate a system time distribution as possible, use multiple NTP servers for an NTP client.

Note: If you switch NTP on (set any value other than off) when SNTP is already active on the device, the device reports an error.

To switch NTP on, first deactivate SNTP.

On delivery, SNTP is switched off.

Protection from Unauthorized Access

5 Protection from Unauthorized